P4     Addressing Nonlinearities in the Observation Operator for    Satellite Cloud-Affected Radiances

Wang, Hongli, and Thomas AulignŽ, National Center for Atmopheric Research

The nonlinearity in the observation operator is addressed within the framework of an Observation System Simulation Experiment (OSSE) for cloud-affected satellite radiance assimilation. This study focuses on various approaches to reduce observation-minus-first-guess departures and improve the tangent-linear approximation for the observation operator with the goal of assimilating cloud-affected radiance observations. The issues addressed are: 1) the ability of the cloud analysis scheme to retrieve the cloud hydrometeor variables, 2) the ability of cloud hydrometeor retrievals to reduce the observation departures and improve the tangent-linear approximation for the observation operator. The OSSE results show that retrieved cloud condensates produced by the adjusted GSI cloud analysis package are very similar to the truth in location and amplitude. Results also show that, compared to the observation departures with a cloud free background, the observation departures with a first guess enhanced by the GSI cloud analysis package are significantly reduced and the tangent-linear approximation for the cloudy radiance observation operator is improved. The improved first guess using the GSI cloud analysis package is expected to improve the cloud hydrometeors analysis in a variational radiance data assimilation system.